Skid steer loaders and multi-terrain loaders are used extensively in construction applications, in agricultural applications, and in other applications where power and versatility are needed. Skid steer loaders and multi-terrain loaders are essentially the same type of machine, with the exception of the ground engagement components. Typically, skid steer loaders move on wheels, while multi-terrain loaders are carried on tracks. However, both types of loaders offer relatively small size and high maneuverability, and can use a wide variety of attachment work tools, making them extremely flexible in application. Skid steer loaders and multi-terrain loaders may be used to dig, to level, to cut, to carry, to load, and to perform any number of other tasks. For each such task, the loader carries a specially designed attachment on the loader arms that extend forward from the loader body.
Skid steer loaders and multi-terrain loaders typically are hydraulically powered. An hydraulic pump, driven by a diesel engine, supplies hydraulic fluid under pressure to various vehicle components. A loader typically has a pair of hydraulic motors that drive the vehicle wheels or tracks. The loader is turned by driving the wheels or tracks at differing speeds. The loader arms that extend forward from the vehicle and to which a bucket, grapple, blade or other attachment is mounted, are also moved by means of hydraulic cylinders that are appropriately configured and controlled by the loader operator. To accomplish this control, the vehicle operator typically uses joy stick controls, or similar controls, in the operator cab.
One significant advantage offered by skid steer loaders and multi-terrain loaders is their ability to carry and operate dozens of different attachments, changing the function of the machine as rapidly as the attachments can be changed. These numerous attachments include augers, bale handlers, brooms, buckets, cold planers, concrete pulverizers, cutters, dozer blades, fertilizer spreaders, fork lift forks, grapples, hitches, landscape rakes, mowers, mulchers, plate compactors, pole claws, pot movers, rock and tree handlers, rock saws, rollers, rotary brooms, shears, snow blowers, splitters, stump grinders, swale blades, tillers, tree spades, trenchers, and winches, among others. Each of these attachments or work tools is unique. Some of the attachments are mounted on the ends of the forward extending loader arms and are simply raised, lowered and reoriented by hydraulic cylinders on the loader that control the position of the arms and the orientation of the attachment coupler at the ends of the arms. Many of the attachments, however, have additional moving elements on the attachment that are powered by one or more hydraulic cylinders carried on the attachment. For example, a grapple attachment may have jaw-like teeth that are moved in relation to each other to grasp an object. One or more hydraulic cylinders are carried on the attachment to effect this movement.
Controlling hydraulic cylinders that are carried on attachments has been problematic. Typically, hydraulic valves on the loader are controlled by an operator to control the flow of hydraulic fluid to the cylinders on an attachment. Because the designs of the various attachments are so diverse, the movement rates of the cylinders on the attachments that is needed or preferred for operation of the attachments may vary significantly. Consequently, the valves must be actuated differently when an operator is controlling various attachments. Movement of an attachment element might, for example, be slower or faster than desired. Similarly, controlling the hydraulic cylinders on the vehicle that control the position of the arms and the orientation of the coupler at the ends of the arms that engages the coupler is also difficult in that the speed of movement and the fluid flow needed to move these cylinders varies among the various attachments. As a consequence, rapid changing of attachments has been made more difficult due to the need to adjust the hydraulics for changes in operation.